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From: Peter Eisentraut <[email protected]>
To: Masahiko Sawada <[email protected]>
To: Andres Freund <[email protected]>
Cc: Ayush Tiwari <[email protected]>
Cc: [email protected]
Subject: Re: tid_blockno() and tid_offset() accessor functions
Date: Fri, 13 Mar 2026 14:27:23 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAD21AoC48MQ4W5vU1ZPaXXtFPtiacEREN_XXrn3SRRku5cighg@mail.gmail.com>
References: <CAJTYsWUzok2+mvSYkbVUwq_SWWg-GdHqCuYumN82AU97SjwjCA@mail.gmail.com>
	<CAD21AoBdgM+4X=Wg0T==C9ahenm2nUb=q5AxxeEb_JVoKOzbgw@mail.gmail.com>
	<fe2ay3acydk6sd3iwkvol7t3kgswzfsuaz2vdgqornx4hg7ji2@dpwilwuzq7a2>
	<CAD21AoC48MQ4W5vU1ZPaXXtFPtiacEREN_XXrn3SRRku5cighg@mail.gmail.com>

On 12.03.26 17:51, Masahiko Sawada wrote:
> On Wed, Mar 11, 2026 at 2:50 PM Andres Freund <[email protected]> wrote:
>>
>> Hi,
>>
>> On 2026-03-11 14:48:08 -0700, Masahiko Sawada wrote:
>>> On Fri, Feb 27, 2026 at 10:59 AM Ayush Tiwari
>>> <[email protected]> wrote:
>>>>
>>>> Hi hackers,
>>>>
>>>> As of now we don't have any built-in way to extract the block and offset components from a TID. When people need to group by page (like for bloat analysis) or filter by specific blocks, they usually end up using the `ctid::text::point` hack:
>>>>
>>>>      SELECT (ctid::text::point)[0]::bigint AS blockno,
>>>>             (ctid::text::point)[1]::int    AS offset
>>>>      FROM my_table;
>>>>
>>>> This works, but it's pretty clunky, relies on the text representation, and isn't great if you're trying to parse TIDs outside of SQL.
>>>>
>>>> The attached patch adds two simple accessor functions:
>>>> - `tid_blockno(tid) -> bigint`
>>>> - `tid_offset(tid) -> integer`
>>>
>>> How about adding the subscripting support for tid data type? For
>>> example, ctid[0] returns bigint and ctid[1] returns int.
>>
>> That just seems less readable and harder to find to me.  I think it'd also
>> make the amount of required code noticeably larger?
> 
> Yeah, using the dedicated functions would be more intuitive than using
> magic numbers 1 and 2, and require less code.

Also, you can use one-argument functions like field names, like 
tid.tid_blockno, so it's definitely more intuitive that way.

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